This disclosure is directed to systems and methods for measuring belt velocity error and reducing torque disturbance in the photoreceptor of image forming devices.
A variety of systems and methods are conventionally used for velocity control in image forming devices. Such systems and methods can include classically designed velocity feedback systems supplemented by a periodic feed-forward control scheme, and feed-forward control algorithms that compensate for an acoustic transfer assist (ATA) vacuum, or drag on the belt, that are disturbed as the belt seam passes over the ATA. This generally involves measuring the transient in belt velocity that is caused by the temporary loss of drag, and commanding the photoreceptor drive motor in a fashion contrary to and simultaneous to the loss in drag. Such a feed-forward control scheme is generally highly effective because the position of the transient is constant, can be tracked as a function of belt position, and varies slowly over time. Moreover, the shape and nature of this disturbance is generally in the form of sin3, so only the height, width and start point of the correction needs to be known.
FIGS. 1 and 2 illustrate a side elevation view and a front elevation view, respectively, of a schematic of a transfer subsystem 100, which includes a photoreceptor belt 110. A photoreceptor belt motor drive unit 122 engages the photoreceptor belt 110 and moves the photoreceptor belt 110 across a series of support rollers 124, 130, 132, 134, 142, 144, 146, and/or a plurality of non-rotating support bars 152, 154, 156, 158.
Typically, photoreceptor belts are fabricated from long sheets of photoreceptor material that are cut to size. The ends of the cut photoreceptor material are welded, or otherwise mated, together in order to form a continuous belt. This fabrication process produces a photoreceptor belt seam 115 at the point where the ends of the photoreceptor belt 110 are welded, or otherwise mated, to be joined together.
Some transfer subsystems, such as the one shown in FIGS. 1 and 2, include an ATA module 120, which draws the photoreceptor belt 110 into a plenum using a vacuum. The ATA module 120 vibrates the photoreceptor belt 110 in the plenum to aid in transferring toner from the photoreceptor belt 110 to an image receiving medium.
In areas of the photoreceptor belt 110 where there is no seam, a tight vacuum is maintained in the ATA module 120. However, when the photoreceptor belt seam 115 of the photoreceptor belt 110 crosses the ATA module 120, the vacuum seal is momentarily broken. Drag of the photoreceptor belt 110 on the photoreceptor belt motor drive unit 122 is momentarily reduced causing the photoreceptor belt motor drive unit 122 to speed up. Speed of the photoreceptor belt motor drive unit 122 must generally be tightly controlled. Photoreceptor belt velocity sensors (not shown) sense the increase in velocity of the photoreceptor belt motor drive unit 122. A motor control device reacts to readjust the speed of the photoreceptor belt motor drive unit 122 and the photoreceptor belt 110.
New U.S. patent application Ser. No. 11/125,103, entitled “Systems and Methods for Determining Feed Forward Correction Profile For Mechanical Disturbances In Image Forming Devices” by James Calamita, filed on May 10, 2005, which is commonly assigned, teaches a control system to automate and/or adapt feed-forward correction (FFC) profile to match precisely the timing and nature of a torque disturbance in a transfer subsystem, which may reduce or substantially nullify torque disturbances, such as, for example, torque disturbances caused by a photoreceptor belt seam passing over an ATA in a photoreceptor belt-based transfer subsystem in an electrophotographic and/or xerographic image forming device. Ser. No. 11/125,103 also provides a learning algorithm using a correlated model of system dynamics to compensate for torque disturbances in mechanical systems, such as, for example, transfer subsystems, in image forming devices.
New U.S. Patent Application entitled “Systems and Methods for Reducing Torque Disturbance in Devices Having an Endless Belt” by Kevin M. Carolan, U.S. Pat. No. 7,157,873 filed on May 5, 2005, which is commonly assigned, teaches a control system to compensate for motion disturbances which may cause defects in multi-color output images produced by image forming devices. The disclosed system may include a controller that determines when a torque disturbance is expected to occur and controls the photoreceptor belt motor drive unit with a compensation amount that may be retrieved from a data structure. This compensation amount from the data structure may be adjusted via a gain factor and may be combined with the output of a closed loop compensator at a summation point, to attempt to minimize the misregistration effect produced by the torque disturbance in the output images produced by the image forming device. U.S. Pat. No. 7,157,873 employs a timing methodology to anticipate the onset of a disturbance and via the controller attempts to insert an opposing profile that causes the photoreceptor belt motor drive unit to generate an opposing torque to substantially nullify the disturbance. Amplitude of a correction profile, corresponding to the amplitude of the disturbance, is manually adjusted to attempt to minimize the effects of the disturbance on the produced output images, for example, the color-to-color registration error. The controller monitors the onset of the disturbance or predicts the onset of the disturbance based on sensed photoreceptor belt position and encoder timing. Correction factors for the current operating state of the transfer subsystem in the image forming device are obtained substantially through a trial and error method.